1. Field of the Invention
The present invention relates to a heat treatment unit used to perform heat treatment on a substrate, and a heat treatment method.
2. Description of the Related Art
In a photo-resist treatment step in a process of semiconductor device fabrication, various kinds of heat treatments, such as heat treatment after a resist-coating on the surface of a semiconductor wafer (described as xe2x80x9ca waferxe2x80x9d hereinafter) called prebaking and heat treatment after an exposure of a pattern called post-exposure baking, are performed.
Such heat treatments are generally performed in a heat treatment unit. The heat treatment unit comprises a disk-shaped heat plate with some thickness made of aluminum in a treatment case, and performs heat treatment on the wafer by putting the wafer, which is to undergo heat treatment, on the heat plate and then by heating the heat plate to a predetermined temperature by a heating element embedded in the heat plate.
Further, there is a case where a temperature during heat treatment varies corresponding to types of semiconductor device to be formed, resist solution and process, such as heating the wafer to 140xc2x0 C. or heating the wafer to a lower temperature, 90xc2x0 C., for example. In this case, when the heat plate which has been undergoing heat treatment at 140xc2x0 C., for example, is changed to the one to be heated at 90xc2x0 C., it is inevitable to once lower the temperature of the heat plate, for example, to 90xc2x0 C. In such situations, a conventional heat treatment unit of this type is not especially provided with a mechanism for cooling, or the like.
It is necessary to vary the temperature of the heat plate since the heat treatment temperature varies corresponding to types of semiconductor device to be formed, resist solution and process. On this occasion, it is preferable to raise and lower the temperature of the heat plate quickly in order to improve a throughput in wafer fabrication.
However, heat exchange is not smoothly performed in such a manner that heat escapes from the outer peripheral portion of the heat plate and below the heat plate when the temperature of the heat plate is raised, and heat is accumulated in the heat treatment unit when the temperature of the heat plate is lowered, thereby requiring long time to raise and lower the temperature of the heat plate.
In addition, when the heat plate is cooled to the predetermined temperature, heat is accumulated not only in a supporting member which supports the heat plate but also in an outer circumferential wall which surrounds an outer circumference of the supporting member if performed simply with spontaneous cooling, which is undesirable since considerably long time is required to make the temperature of the surface portions of the heat plate uniform after the heat plate is heated up to the predetermined temperature.
An object of the present invention is to provide a heat treatment unit in which a temperature of a heat plate can be raised and lowered quickly compared with the conventional heat treatment unit, and a heat treatment method.
A first aspect of the present invention is a heat treatment unit in which a substrate is heated on a heat plate, comprising a supporting member which supports at least the peripheral portion of the heat plate, material of the supporting member being thermal insulating material.
A second aspect of the present invention is a heat treatment unit in which a substrate is heated on a heat plate, comprising a supporting member which supports at least the peripheral portion of the heat plate, material of the supporting member being thermal insulating material, and further comprising gas supply means for blowing gas for cooling against the reverse side of the heat plate.
A third aspect of the present invention is a heat treatment unit in which a substrate is heated on a heat plate, comprising an outer circumferential wall surrounding the outer circumference of a supporting member which supports the heat plate, and a fin provided on the surface of the outer circumferential wall.
A fourth aspect of the present invention is a heat treatment unit in which a substrate is heated on a heat plate, comprising an outer circumferential wall surrounding the outer circumference of a supporting member which supports the heat plate, and a tube provided to have contact with the surface of the outer circumferential wall, in which fluid for cooling circulates.
A fifth aspect of the present invention is a method of heating with a substrate placed on a heat plate, comprising the steps of closing a space below the heat plate when the substrate is heated and opening the space below the heat plate when the heat plate is cooled.
According to the present invention, heat accumulated in the heat plate can be inhibited from dissipating from the outer peripheral portion of the heat plate since material of the supporting member is thermal insulating material, whereby a temperature of the heat plate can be raised quickly while the temperature of the surface portion of the heat plate can be kept uniform during heat treatment.
According to the present invention, by blowing gas for cooling against the reverse side of the heat plate, heat accumulated in the heat plate is rapidly diminished by the gas when the heat plate is cooled, thereby enabling the heat plate to be cooled more quickly than the conventional one.
Further, according to the present invention, heat capacity of the outer circumferential wall can be decreased by virtue of the fin provided on the surface of the outer circumferential wall. Furthermore, the surface area of the outer circumferential wall is increased, which improves the heat-dissipation efficiency of heat which is accumulated in the outer circumferential wall. As a result, the heat plate supported by the supporting member can be more quickly cooled than the conventional one.
According to the present invention, heat accumulated in the outer circumferential wall is rapidly diminished since a tube, in which fluid for cooling circulates, is provided, thereby improving a speed of lowering the temperature of the heat plate arranged inside of the outer circumferential wall, compared with the conventional one.
According to the present invention, when the substrate is heated, the substrate can be heated at a predetermined temperature by closing a space below the heat plate to retain heat therein, which makes it possible to raise the temperature more quickly than the conventional one. When the heat plate is cooled, it is possible to lower the temperature more quickly than the conventional one since the space below is opened. Therefore, it takes less time to change setting of temperature of the heat plate, resulting in the improvement of a throughput.